The invention is directed to the problem of efficient use of space in an electronic system that has circuit cards housed in a card cage. More particularly, the invention is directed to the efficient use of space in the design of the card cage and the card guides of the cage and especially the mounting of the card guides on the card guide cage.
FIG. 1 shows a cross-sectional side view of a typical prior art card guide arrangement. Circuit card 10 is held in place on a card cage 11 by a card guide 12. The card cage 11 is part of an arrangement, e.g. a standard 20xe2x80x3 card rack, for housing the circuit cards of an electronic system. The card guide 12 is made from a material that is flexibly resilient, e.g. plastic. The card guide 10 is held in place on the card cage 11 by two or more mushroom headed mounting lugs 13, 14. The lugs are compressible by the nature of their shape and the flexibly resilient material of which the guide is composed so as to fit through respective apertures in the card cage and expanding back to their original shape after insertion, thereby affixing the card guide to the card cage. Typically, one of the apertures, aperture 15, is circular for precisely locating the guide on the cage, while the other aperture, aperture 16 is oblong, which allows relative movement between the remainder of the guide and the cage. This allowance is necessary to accommodate different amounts of expansion and contraction of the card and guide due to normal thermal cycling during operation of the electronic system however, this allowance has some times allowed the guide to detach from the cage due to normal thermal cycling.
Referring to FIGS. 2A and 2B (which correspond to FIGS. 3 and 4 of U.S. Pat. No. 3,878,438 entitled Printed Circuit Card Guide), the card guide 20 has depending tabs 25, 28 at the lateral ends which fit into apertures in the card cage 31, 32, 33. Tabs 25, 28 protrude below the surface of the card cage into the card case interior and therefore do not achieve space savings. Moreover, the central portions of the card guide 20 are not secured to the card cage.
Referring now to FIG. 3 (which corresponds to FIG. 5 of U.S. Pat. No. 4,327,835 entitled xe2x80x9cUniversal Snap-In Card Guide for Printed Circuit Card Enclosures,xe2x80x9d) the card guide 34 has tabs 35, 36 at each end which fit into apertures 37, 38 in the card cage 39. As in the case of FIGS. 2A and 2B, the tabs 35, 36 protrude below the surface of the card cage into the card cage interior and therefore do not achieve the desired space savings.
U.S. Pat. No. 5,738,226 issued to Dean on Apr. 14, 1998 entitled xe2x80x9cGuide Piece and Method for Mounting to a Chassis in Multiple Orientationsxe2x80x9d discloses a card guide. This patent is directed to the same problem of eliminating the protrusion of the guide mounting means to the card chassis/cage (albeit for a different reason). This patent uses tabs on one surface of the card guide that engage fingers on the card cage and nubs on another surface on a guide that engages with holes on the card cage to mount the guides in a manner that eliminates the protrusions. However, unlike the present invention in which the tabs, fingers and arches provide alignment locking all on one side of the cage mount, the prior art requires additional fingers to provide alignment and locking to complete the alignment in the locking means.
Typically, the retention pins protrude about xe2x85x9xe2x80x3 below the card cage, which is an area that is often required for EMI shielding. Since there are two guides (an upper and a lower) required for each card, the space required for retention pins in a 20xe2x80x3 rack having four layers of circuit cards would be 1xe2x80x3 (2xc3x974xc3x97xe2x85x9xe2x80x3), or about 5% of the height of the rack. Since space is usually at a premium in electronic systems, any space savings can be valuable and provide a commercial advantage to the systems, e.g. by allowing the size of the circuit cards to be increased thereby enabling more functionality to be fit onto a card.
The object of the present invention is to provide an improved circuit card mounting guide and method of installing the card guide on a card cage or frame.
The invention features a circuit card guide for mounting onto a member of a circuit card cage, comprising: an elongated body of a flexibly resilient material having a groove extending along its longitudinal axis for receiving the edge of a printed circuit card, the groove being open at least at one end of the elongated body; and first and second outer surfaces extending along the longitudinal axis and being opposite to each other with respect to the groove, each outer surface having a tab disposed adjacent each end of the elongated body, each tab adapted to be received by fingers on the member; whereby flexing the circuit card guide about the longitudinal axis allow the tabs to be received by the member and allowing the circuit card guide to return to an unflexed state securely mounts the circuit card guide onto the member.
The invention also features:
1. Coplanar tabs which extend perpendicular to the first and second outer surfaces,
2. One of the first and second outer surfaces has a medial tab disposed at a location substantially halfway between the ends of the elongated body for being received by the member when the guide is in the unflexed state.
3. A ramp provided at the open end for slidably receiving a circuit card.
4. A circuit card guiding flare is formed in the groove at the open end.
The invention further features a circuit card cage for housing circuit cards, comprising: a circuit card guide; and a cage frame member having mounting means for mounting a plurality of circuit card guides, the circuit card guides being as described above.
Flexing the circuit card guide about the longitudinal axis allows the tabs to be received by the mounting means and allowing the circuit card guide to return to an unflexed state securely mounts the circuit card guide onto the member.
The invention also features:
1. The cage mounting structure comprises two pairs of fingers for engaging the end tabs, the fingers of each pair being pointed toward the other pair and parallel to the longitudinal axis of the circuit card guide in a mounted position on the member, so no part of the card guide protrudes below the mounting structure surface.
2. Each finger of a pair registers with a respective one of the first and second outer surfaces to alleviate movement of the guide relative to the cage member that is transverse to the longitudinal axis.
3. The pairs of fingers are spaced apart relative to each other such that movement of the card guide relative to the cage member that is along the longitudinal axis is allowed to accommodate differences in thermal expansion and contraction of the circuit card guide and cage member.
4. The tabs extend perpendicular to the first and second outer surfaces.
5. One of the first and second outer surfaces has a medial tab disposed at a location substantially halfway between the ends of the elongated body for being received by a corresponding medial arch of the cage member when the guide is in the unflexed state.
A further feature of the invention is in the method of installing or mounting the card guide on the card guide cage. According to this feature of the invention, there is provided on the surface of the card cage two pairs of end fingers and a medial arch proximate the center of the card cage member. The method comprises first engaging one of the end tab pairs with an end finger pair, flexing the card guide in the plane thereof to engage the other end tab pair with the second set of end fingers at the opposite end thereof. The card guide is then flexed out of the plane thereof so as to permit a medial tab to engage a medial arch member. Thus, the card guide is mounted on the card guide cage by first seating the pairs of end tabs in the end finger pairs by first flexing in the direction of the plane of the card guide and then after seating the end tabs in the end tab fingers, the card guide is flexed out of the plane thereof so as to permit the medial tab to seat under its corresponding medial arch.